Long records of sea level show decadal and multi-decadal oscillations of synchronous and asynchronous phases, which cannot be detected in short-term records. It is clear from the analyses of the tide gauges of long datasets that the sea level has been oscillating about the same almost perfectly linear trend line all over the 20th century and the first 17 years of this century. The tide gauge information does not support any claim of rapidly changing ice mass in Greenland and Antarctica. The average of four long global datasets gives a sea level rise of 1.3 mm/yr with an acceleration of 0.005 mm/yr, which is statistically insignificant.

European sea level records are among the best to detect an acceleration due to climate change. This paper by Watson 2017 used advanced techniques to analyze 83 long tide gauge station records across Europe. Most of the records are more than 100 years. The abstract states “Key findings are that at the 95% confidence level, no consistent or compelling evidence (yet) exists that recent rates of rise are higher or abnormal in the context of the historical records available across Europe, nor is there any evidence that geocentric rates of rise are above the global average. It is likely a further 20 years of data will distinguish whether recent increases are evidence of the onset of climate change–induced acceleration.” In other word, the data shows no indication of an AGW induced sea level rise acceleration.

This open access paper by Beenstock et al show that tide gauge locations in 2000 were independent of sea level rise (SLR) as measured by satellite altimetry. Therefore these tide gauges constitute a quasi-random sample, and inferences about global SLR obtained from them are unbiased. The global mean SLR is 0.39–1.03 mm/year. The paper says "the claim that sea levels are rising globally (IPCC 2014) is an artifact induced by the use of imputed data."

Some computer models predict 1 metre sea level rise by the end of the 21st century. However, the actual experimental data shows, at most, a slow and modest increase in sea levels, which seems completely unrelated to CO2 concentrations. The main estimates of long-term sea level changes are based on data from various tidal gauges located across the globe. These estimates apparently suggest a sea level rise of about 1 to 3 mm a year since records began. Importantly, the rate still seems to be about the same as it was at the end of the 19th century, even though carbon dioxide emissions are much higher now than they were during the 19th century.

There is currently a debate in the Netherlands about the future rate of sea level rise. Independent researchers estimate that the sea level will rise 20 cm to the end of the century, while the IPCC expects about 50 cm. A government commission recommends an expenditure of 80 billion euros over the next 40 years to raise dikes based on a high case sea level rise prediction of 110 cm by 2100.